Metal-Ligand Electron Transfer in 4d and 5d Group 9 Transition Metal Complexes with Pyridine, Diimine Ligands

Our recent results of the chemistry of group 9 Rh and Ir metal complexes bearing the ubiquitous pyridine, diimine (PDI) terdentate nitrogen donor are reviewed. Examples reflecting the special nature of the PDI ligand include a facile C-H activation process and the stabilization of a very rare late transition metal iridium nitrido compound, (PDI)Ir N, and its direct hydrogenation to the corresponding amido complex according to (PDI) Ir N + H-2 -> (PDI)Ir-NH2. The amount of electron transfer to the PDI ligands in (PDI) Rh, Ir-R,X complexes encompassing a variety of R, X ligands with weak/strong sigma- and sigma-donors/acceptors was analyzed in terms of the innocence of the PDI ligand. With this regard, a combination of DFT methods, X-ray-crystallographic data, and, in particular, C-13 NMR spectroscopy was employed for a series of square-planar Rh and Ir complexes including a large number of new representatives. Their syntheses, spectroscopic characterization, and X-ray crystal structures are reported.